Radiofrequency amplification system



Oct. 8, 1929. v. H. LAUGHTER RADIO FREQUENCY AMPLIFICATION SYSTEM Filed Nov. 5, 1925 Patented Oct. 8, 1929 UNITED STATES PATENT OFFICE VICTOR H. LAUGHTER, OF ST. LOUIS, MISSOURI, ASSIGNOR TO VALLEY ELECTRIC COMPANY, OF ST. LOUIS, MISSOURI, A CORPORATION OF DELAWARE RADIOFREQUENCY AMPLIFICATION SYSTEM Application filed November 5, 1925.

This invention relates to radio frequency amplification systems, and more particularly to those utilizing audions or electron tubes.

One of the objects of this invention is to provide means for preventing undesirable oscillations in the circuit.

Another object is to provide means for suppressing any oscillation which may be or tend to be set up.

Another object is to provide a system in which the oscillation is suppressed by a potential action rather than by capacity action.

Another object is to provide a multi-stage radio frequency amplification system employing toroidal transformers.

Further objects will appear from the detail description taken in connection with the accompanying drawing, in which:

Figure 1 is a diagram showing a radio fre- 2 quency amplification system embodying this invention;

Figure 2 is a side elevation of a radio frequency transformer showing the coupling element;

Figure 3 is a section on line 33, Figure 2; and

Figure 4 is a detail showing another embodiment of this invention.

In accordance with this invention a cou- 0 pling element is connected with the grid of an audion of a radio frequency amplification system and is electrostatically coupled with the plate circuit so as to apply to the grid a potential which is opposed to the potential of the disturbing oscillation. This coupling elementis electrostatically coupled to a coil, preferably in the out-put circuit, and which coil is preferably the secondary or primary of the radio frequency transformer if! the output circuit of the audion, to the grid of which the coupling element is connected. The c0upling element is preferably an open-ended coil which is magnetically coupled with a primary or secondary orboth, of the radio frequency transformer and is arranged for adjustment so as to vary the potential impressed on the grid.

While the radio frequency transformer or the coil to which the coupling element is 50 coupled may be of the usual cylindrical or Serial No. 67,107.

solenoid type, a toroidal coil transformer may be used and the coupling element or coil is arranged for adjustment with respect to the magnetic field of the transformer coil or coils seals to vary the potential impressed on the gri Referring now to the accompanying drawing, and more particularly toFigure 1 which shows a radio-receiving system having two stages of radio frequency and two stages of audio frequency, 1 and 2 designate the amplifier tubes in the radio frequency circuit, 3 the detector tube, and 4 and 5 the amplifier tubes in the audio frequency circuit. The audion tubes are of the usual form having a filament, a grid and a plate. The radio frequency transformers are indicated at 10, 20 and 30, while the audio frequency transformers are indicated at 40 and 50. Associated with the in-put circuit of each tube is a variable condenser indicated at 11, 21 and 31. The usual grid leak and condenser is shown at 6 and the current controlling rheostats at 7 and 8. Condensers 12 and 22 may also be provided. The usual connections to the aerial and ground and the A battery, B battery and C battery are also indicated.

Connected with the grid of each of the audions 1 and 2 in the radio frequency circuit, is a coupling element 9, which as heretofore described, is preferably an open-ended coil. This coil is preferably magnetically coupled with the radio frequency transformer between the tube to whose grid it is connected and the succeeding tube, and since it is in close proximity thereto, it is also electrostatically coupled with the transformer coils. The coil 9 is so wound that the voltage set up therein and impressed on the grid will be opposed to the disturbing voltage tending to set up the oscillation, so that the oscillation will be suppressed. It is furthermore adjustable in order to vary the magnitude of the impressed voltage in order to balance the objectionable voltage.

While, as stated, the invention is applicable to radio frequency amplification systems employing cylindrical or solenoid coils, toroidal coils may be used for the radio frequency transformers. Referring to Figures 2 and 3, both the primary and the secondary coils are shown as of toroidal form, the primary being made of sections 14 interposed between the sections 15 of the secondary. These coils are held in proper assembled relation by endpieces 16 having notches 17 for engaging the coil sections and held together by a screw 18 passing through a collar 19. Tape or ribbon 24 may also be provided to further hold the parts together, while the end plates are provided with feet 25 for attaching the trans former to its support.

Mounted on one of the end plates 16 is a slotted bracket 26 supporting the coil 9 and held in adjusted position by a screw 27 taking into the end plate. In this way the coil 9 can be adjusted within the field set up by the primary and secondary coils. By moving the coil 9 radially the voltage set up therein and impressed on the grid can be varied and adjusted.

It will thus be seen that the invention accomplishes its objects. The provision of the coupling element 9 impresses on the grid a voltage which will suppress the oscillation set up or tending to be set up. By adjust ment of this coil, the voltage impressed on the grid can be varied until the proper balance is obtained. The direction of winding of the coil 9 can, or course, be readily determined, for if wound in one direction it will cause suppression of the oscillation, while if wound in the wrong direction the oscillation will not be completely suppressed. In the diagram as shown in Figure 1, and in Figures 2 and 3, the turns of the coupling coil are in the same direction as those of the primary and secondary of the transformer to which the coil is coupled. It is not, however, neces sary to provide a condenser in the lead from this coil to the grid, for a voltage of the proper value can be readily obtained by adj ustment of the coil. In view of the fact that the coil is an open-ended coil, the coupling to the output circuit of the audion tube, to the grid of which this coil is connected, is an electro-static as well as magnetic coupling. Accordingly the phase as well as the magnitude of the voltage applied to the grid is con trollable as well as adjustable. Moreover since the coil is coupled electro-statically as well as magnetically to the transformer coil or coils, the adjustment provides in effect a tapped coupling. WVhile the adjustment of the coil 9 is critical, the number of turns of this coil is not critical in suppressing oscillations. However, by providing a coupling coil with a number of turns (twelve turns of line wire being found satisfactory where the primary has twenty-one turns and the secondary one hundred sixty five turns and where the parts are of the relative dimensions as shown, when using ordinary audions), the tone quality is improved; accordingly the combination results in a clean, pure tone with a comparatively wide range of selectivity.

The employment of toroidal coils in the radio frequency transformer is advantageous, particularly in multi-stage radio frequency amplification. As is well known, shielding must frequently be resorted to in order to prevent interaction of the transformer lieldsof the several transformers, due to magnetic leakage. While this can be overcome to some extent by placing of the coils of solenoid or cylindrical transformers at definite angles, this is not always convenient. In a toroidal coil, however, the field is substantially enclosed by the coil and magnetic leakage is minimum. Accordingly the employment of toroidal coil transformers in a multistageradio frequency amplification circuit is especially desirable since it enables these coils to be placed inthe most desirable relation without interference.

Where cylindrical or solenoid coil transformers are used, as shown in Figure 4, which is a detail section of a transformer, the usual tube 51 of insulating material may have the primary 14 and secondary 15 of the required number of turns. The tertiary or coupling coil 9 may be wound on a band 52 of insula ing material, which may have a close enough fit with the primary so as to be slidable therealong'and yet be held frictionally in any adjusted position. In this way the coupling coil can be adjusted to the desired position and held in adjusted position.

'While certain theories have been advanced with reference to the operation, it is to be understood that they are not absolutely necessary to the practical operation of this system; accordingly it is to be understood that this invention is not to be limit-ed to any particular theory of operation. It is further obvious that various changes may be made in details of construction without departing from the spirit of this invention; it is, therefore, to be understood that this invention is not to be limited to the specific details shown and described.

Having thus described the invention, what is claimed is:

1. A radio frequency amplificationsystem comprising, an audion having a grid and a plate, an input circuit-,an output circuit, a coil in said latter circuit, and a coil connected with said'grid and electrostatically and electrornagnetically coupled with said plate circuit, said latter coil being adjustable relative to said first coil.

2. A radio frequency amplification system comprising, an audion having a grid and a plate, an input circuit, an output circuit, one of said circuits having a coil, and an open ended coil connected with said grid and magnetically and electrostaticallycoupled with said first coil, said open-ended coil being adjustable relative to said first coil.

3. A radio frequency amplification system comprising, an audion having a grid and a plate, a grid circuit, a plate circuit having a transformer, and a coil connected with said grid and electrostatically and electromagnetically coupled with said transformer, said coil being adjustable relative to said transformer.

4. A radio frequency amplification system comprising, an audion having a grid and a plate, an input circuit, an output circuit, having a coil, an open-ended coil connected with said grid and magnetically and electrostatically coupled with said first coil, and means for adjusting said open-ended coil relative to said first mentioned coil.

5. A radio frequency amplification system comprising, an audion having a grid and a plate, an input circuit, an output circuit, a toroidal coil in one of said circuits, and a coil connected with said grid and magnetically and electrostatically coupled in adjustable relation to said toroidal coil.

6. A multi-stage radio frequency amplification system comprising a plurality of audions each having a grid and a plate, input and output circuits, a coil in each output cir cuit, and a coil connected with the grid of each audion and electrostatically and electromagnetically coupled with its plate circuit, said latter coil being adjustable relative to said first coil.

In testimony whereof I aflix my signature this 5th day of Sept, 1925.

VICTOR H. LAUGHTER. 

